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Tuesday, May 13, 2014

NASA: Antarctic Glacial Melting Past Point of No Return

PASADENA, California -- Glacial melting on a section of the West Antarctic Ice Sheet has passed the point of no return, according to NASA scientists.

Researchers say that a new study presents multiple lines of evidence, incorporating 40 years
of observations, that indicate the glaciers in the Amundsen Sea sector
of West Antarctica are in an irrevisable decline.

According to NASA, that these glaciers already contribute significantly to sea level rise,
releasing almost as much ice into the ocean annually as the entire
Greenland Ice Sheet. They contain enough ice to raise global sea level
by 4 feet (1.2 meters) and are melting faster than most scientists had
expected.

Eric Rignot, of UC Irvine and NASA's Jet
Propulsion Laboratory said these findings will require an upward revision to
current predictions of sea level rise. "This sector will be a major contributor to sea level rise in the
decades and centuries to come," Rignot said. "A conservative estimate is
it could take several centuries for all of the ice to flow into the
sea."

The glaciers flow out from land to the ocean, with their leading
edges afloat on the seawater. The point on a glacier where it first
loses contact with land is called the grounding line. Nearly all glacier
melt occurs on the underside of the glacier beyond the grounding line,
on the section floating on seawater.

Just as a grounded boat can float again on shallow water if it is
made lighter, a glacier can float over an area where it used to be
grounded if it becomes lighter, which it does by melting or by the
thinning effects of the glacier stretching out. The Antarctic glaciers
studied by Rignot's group have thinned so much they are now floating
above places where they used to sit solidly on land, which means their
grounding lines are retreating inland.

The accelerating flow speeds and retreating grounding lines reinforce
each other. As glaciers flow faster, they stretch out and thin, which
reduces their weight and lifts them farther off the bedrock. As the
grounding line retreats and more of the glacier becomes waterborne,
there's less resistance underneath, so the flow accelerates.

"The collapse of this sector of West Antarctica appears to be
unstoppable," Rignot said. "The fact that the retreat is happening
simultaneously over a large sector suggests it was triggered by a common
cause, such as an increase in the amount of ocean heat beneath the
floating sections of the glaciers. At this point, the end of this sector
appears to be inevitable."